This invention relates to an electron tube, notably an X-ray tube, comprising a cathode arrangement which includes an electron emitter which is connected to supporting pins which in turn are each connected to the cathode arrangement via a respective fixing element.
An electron tube of this kind, that is to say an X-ray tube, is known from JP-A 63-105427. Therein, the electron emitter, being a directly heated filament, is first connected to a respective supporting pin at both its ends. The supporting pins are introduced into a respective hollow-cylindrical fixing element, the two fixing elements being embedded in a ceramic body. The unit thus formed is moved, by means of a positioning device, to a defined position relative to the cathode head and is fixed in this position.
In order to ensure a defined size and shape of the focal spot produced on the anode by the cathode, the electron emitter must occupy an accurately defined position relative to the focusing electrode even when the filament has been subjected to a thermal treatment. However, during such a thermal treatment the position of the filament may change, so that subsequent to a thermal treatment it is necessary to adjust the position of the electron emitter relative to the focusing electrode. Such adjustment requires skilled labour and is time consuming, notably when the thermal treatment and readjustment must be repeated.
In order to simplify the adjustment operations, EP-A 273 162 discloses the use of a two-part cathode head. Therein, the electron emitter or the supporting pins supporting it are first mounted in the one cathode part in which the filament is suitably accessible from the outside. The two cathode pans are joined only after execution of the thermal treatment and the adjustment.
During adjustment either the electron emitter or at least one of the pins supporting it is bent near its upper end until the electron emitter has reached the desired position.